In the case of gas bags so far proposed having a discharge opening whose cross section is adapted to be varied, the discharge opening is arranged concealed in the gas bag fabric in a section thereof which is puckered up by a rippable seam. Such rippable seam is destroyed when a certain gas pressure within the gas bag is reached so that it is only at this interior pressure level the discharge opening is cleared and the gas may flow out from the interior of the gas bag in order to reduce the internal pressure of the gas bag. Owing to the reduced internal pressure, the gas bag becomes softer.
Conventional forms of gas bag restraining systems are designed for an average body weight. However, for an optimum restraining action, the gas bag should be softer in the case of lighter occupants, whereas, in the case of a larger body weight, a harder gas bag is required in order to fully prevent impact through the gas bag.